Existing well logging devices can provide useful information about hydraulic properties of formations, such as pressures and fluid flow rates, and can obtain formation fluid samples for uphole analysis. Reference can be made, for example, to U.S. Pat. Nos. 3,934,468 and 4,860,581. In a logging device of this general type, a setting arm or setting pistons can be used to controllably urge the body of the logging device against a side of the borehole at a selected depth. The side of the device that is urged against the borehole wall includes a packer which surrounds a probe. As the setting arm extends, the probe is inserted into the formation, and the packer then sets the probe in position and forms a seal around the probe, whereupon formation pressure can be measured and fluids can be withdrawn from the formation.
In certain prior art application of formation testing, a gravel pack is provided at the place where the formation is perforated, to help maintain the integrity of the perforation and to prevent sand from clogging the opening. This gravel pack is generally not made too fine, as it would then tend to clog easily. From experience, it has been recognized that even when a gravel pack is employed at the probe, some sand tends to flow with fluid being sampled. This sand can cause problems with down hole pumps either plugging or by compromising the seals in the pump. As a result of the sand entering the pump, formation tester logging jobs may have to be terminated prematurely or multiple trips in the well may be necessary to acquire all the desired fluid samples. In addition, sampling during cased hole formation tester jobs can be compromised due to metal shavings from the casing entering the formation tester's down hole pump.
It is among the objects of the present invention to address this problem of prior art formation testing tools.
It is also among the objects of the present invention to improve formation testing methods and equipment to obtain enhanced information about the nature of formations being tested, including characteristics of solid components of the formations being tested.